There are known several mechanisms for sharpening knives and the like; some are portable, some are stationary. In the portable structures one problem that has been encountered is that the hone stone will eventually wear at given locations and must be discarded. Most prior art sharpeners provide a honing stone that is permanently attached to the sharpener. Thus, when the stone becomes worn and expended, the entire device becomes worn and expended and therefore is disposed of. An additional problem with prior art portable sharpeners is that the fingers of the user are exposed to the knife during the sharpening or honing operation. Other devices do not provide adequate guides for the knife blade. Thus, uneven and inconsistent sharpening usually occurs. Several sharpeners comprise an elongated sharpening rod extending out from a handle. The knife to be sharpened is then manipulated up and down the sharpening rod in random strokes or movements until the desired edge sharpening occurs. This type of honing is imprecise and does not result in controlled sharpening. While use of this rod type device can result in sharpening, the fingers of the user are exposed, uneven sharpening can occur and wear on the abrasive rod eventually means discarding the entire device.
Typical known other sharpening devices are disclosed in U.S. Pat. Nos. 3,871,141; 4,197,677; 4,291,506 and 4,991,357. In U.S. Pat. No. 3,871,141 (Bonapace) a knife sharpener is disclosed having a flexible band of a fine grain abrasive surface, a frame for mounting the band in a generally V shape and a compression spring within the frame for maintaining the band under tension while permitting the band to yield when a knife is applied thereto. The band is flexible to permit the angle and lateral position of the sides thereof to conform to the angle and force at which the knife is applied thereto. In this type device the sharpening is not guided at all thus allowing the angle of sharpening to be as inconsistent as the inconsistency of the user's strokes against the flexible band. Also, the size of this type sharpener makes it inconvenient to carry such as on camping trips, etc.
In U.S. Pat No. 4,197,677 (Graves) another type sharpener is disclosed having a cylindrical sharpening rod to which a pair of conical guide members have been fixed on either end. A handle extends out from one of the guide members for proper support during the honing operation. The rod is constructed of a ceramic material containing strong abrasives. One hand of the user grips the handle so that the other hand can be used to draw the blade simultaneously along the rod and along the blade from near the blade handle toward the blade tip. No precise guides are provided in this type sharpener only the blade is positioned flat against the conical surface of a guide and that angle is attempted to be manually maintained during each succeeding sharpening stroke. Effectiveness of the sharpening will vary from operator to operator and could not effectively be used by an apprentice who may sharpen at angles other than the proper one. This type device, because of its shape and size, is also cumbersome to carry during hunting, fishing and other type recreational trips.
In U.S. Pat. No. 4,291,506 (Kramm) a hone stone is described having the stone mounted into an expandable stone receiving assembly. The assembly comprises a relatively rigid body having end regions that are convex cylindrical surfaces. A cavity defined by these surfaces receives the stone so that a working face of the stone is exposed. Slots are defined in each end region which extend in the direction of the stone which define a pair of resilient bifurcated portions in each end region to provide also a firm frictional engagement between the hone stone assembly and the honing head. Guide portions to control the sharpening angle are not provided in this type sharpener to maintain a consistent sharpening angle and generally uniform results. Also, no hand protection is provided in Kramm's device.
Some knife sharpeners do provide for removable stones such as in U.S. Pat. No. 4,991,357 (Stickles). In Stickles a case defining a hollow trough is provided where the width of the bottom portion of the trough is slightly less than the width of a stone that can be removably seated therein. Blade support surfaces that are angled upwardly and outwardly surround the seated stone whereby a knife blade is held flatwise against either blade support surface. Protection for the fingers of the user would enhance the type of sharpener disclosed by Stickles.
Thus, a permanent, portable sharpener having interchangeable or removable stones with appropriate guides and hand guards and that is relatively inexpensive would be a significant improvement over the known prior art.